Nerve Tissue The fourth major class of vertebrate tissue is nerve tissue cable 49.5). Its cells include neurons and neuroglia, or sup porting cells. Neurons are specialized to produce and con- duct electrochemical events, or "impulses. "Each neuron consists of three parts: cell body, dendrites, and axon(fig Nucleus ure 49.12). The cell body of a neuron contains the nucleus Dendrites are thin, highly branched extensions that receive incoming stimulation and conduct electric events to the cell body. As a result of this stimulation and the electric events produced in the cell body, outgoing impulses may be pro- duced at the origin of the axon. The axon is a single exten- Axon sion of cytoplasm that conducts impulses away from the cell body. Some axons can be quite long. The cell bodies of neurons that control the muscles in your feet, for example, lie in the spinal cord, and their axons may extend over a meter to your feet Neuroglia do not conduct electrical impulses but instead support and insulate neurons and eliminate foreign materi Is in and around neurons. In many neurons, neuroglia cells ssociate with the axons and form an insulating covering, a myelin sheath, produced by successive wrapping of the membrane around the axon(figure 49. 13). Adjacent neu- moglia cells are separated by interruptions known as nodes of Ranvier, which serve as sites for accelerating an impulse (see chapter 54) The nervous system is divided into the central nervous system(CNS), which includes the brain and spinal cord, and the peripheral nervous system(PNS), which includes nerves and ganglia. Nerves consist of axons in the PNS that are bundled together in much the same way as wires are bundled together in a cable Ganglia are collections of neu- ron cell bod There are different types of neurons, but all are specialized to receive, produce, and conduct electrical signals. Neuroglia do not conduct electrical impulses but have various functions, including insulating axons to accelerate an electrical impulse. Both neurons and neuroglia are present in the CNS and the PNS FIGURE 49.12 A neuron has a very long projection called an axon. (a)A nerve impulse is received by the dendrites and then passed to the cell body and out t through the axon. (b) Axons can be very long single axons extend from the skull down several meters through a giraffe's neck to its pelvis 996 Part XIlI Animal Form and Function
Nerve Tissue The fourth major class of vertebrate tissue is nerve tissue (table 49.5). Its cells include neurons and neuroglia, or supporting cells. Neurons are specialized to produce and conduct electrochemical events, or “impulses.” Each neuron consists of three parts: cell body, dendrites, and axon (figure 49.12). The cell body of a neuron contains the nucleus. Dendrites are thin, highly branched extensions that receive incoming stimulation and conduct electric events to the cell body. As a result of this stimulation and the electric events produced in the cell body, outgoing impulses may be produced at the origin of the axon. The axon is a single extension of cytoplasm that conducts impulses away from the cell body. Some axons can be quite long. The cell bodies of neurons that control the muscles in your feet, for example, lie in the spinal cord, and their axons may extend over a meter to your feet. Neuroglia do not conduct electrical impulses but instead support and insulate neurons and eliminate foreign materials in and around neurons. In many neurons, neuroglia cells associate with the axons and form an insulating covering, a myelin sheath, produced by successive wrapping of the membrane around the axon (figure 49.13). Adjacent neuroglia cells are separated by interruptions known as nodes of Ranvier, which serve as sites for accelerating an impulse (see chapter 54). The nervous system is divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which includes nerves and ganglia. Nerves consist of axons in the PNS that are bundled together in much the same way as wires are bundled together in a cable. Ganglia are collections of neuron cell bodies. There are different types of neurons, but all are specialized to receive, produce, and conduct electrical signals. Neuroglia do not conduct electrical impulses but have various functions, including insulating axons to accelerate an electrical impulse. Both neurons and neuroglia are present in the CNS and the PNS. 996 Part XIII Animal Form and Function Cell body Nucleus Axon Dendrites (a) (b) FIGURE 49.12 A neuron has a very long projection called an axon. (a) A nerve impulse is received by the dendrites and then passed to the cell body and out through the axon. (b) Axons can be very long; single axons extend from the skull down several meters through a giraffe’s neck to its pelvis
e Issue SENSORY NEURONS Cell body Eyes; ears; surface of skin Function from sensory receptors to ( s condition and external environment; send ir Receive information about bodv's Characteristic Cell Types Dendrite Axon Rods and cones; muscle stretch receptors MOTOR NEURONS Typical Location Axo Brain and spinal cord Stimulate muscles and glands; conduct impulses out of CNS toward muscles and glands Characteristic Cell Types Motor neurons Cell body ASSOCIATION NEURONS Dendrites Brain and spinal cord Function Integrate information; conduct impulses between neurons within CNS Characteristic Cell Types Association neurons Nucleus Node of ranvier Axon Neuroglia- FIGURE 49.13 A myelinated neuron. Many dendrites Myelinated region arise from the cell bodv as does a single long axon In some neurons pecaalied for rapid signal conduction the axon is encased in a myelin sheath that is interrupted at intervals. At its far end, the axon may branch to terminate Dendrite on more than one cell Axon Chapter 49 Organization of the Animal Body 997
Chapter 49 Organization of the Animal Body 997 Table 49.5 Nerve Tissue Cell body Dendrite Axon Cell body Dendrites Axon Axon Dendrites Cell body SENSORY NEURONS Typical Location Eyes; ears; surface of skin Function Receive information about body’s condition and external environment; send impulses from sensory receptors to CNS Characteristic Cell Types Rods and cones; muscle stretch receptors MOTOR NEURONS Typical Location Brain and spinal cord Function Stimulate muscles and glands; conduct impulses out of CNS toward muscles and glands Characteristic Cell Types Motor neurons ASSOCIATION NEURONS Typical Location Brain and spinal cord Function Integrate information; conduct impulses between neurons within CNS Characteristic Cell Types Association neurons Cell body Dendrite Axon Nucleus Node of Ranvier Myelin sheath Myelinated region Axon Neuroglia cell FIGURE 49.13 A myelinated neuron. Many dendrites arise from the cell body, as does a single long axon. In some neurons specialized for rapid signal conduction, the axon is encased in a myelin sheath that is interrupted at intervals. At its far end, the axon may branch to terminate on more than one cell
Chapter 49 www.mhhe.com/raven6ch/resource28.mhtml Summary Questions Media resources 49.1 The bodies of vertebrates are organized into functional systems The vertebrate body is organized into cells, tissues 1. What is a tissue? What is an 陈 Art Activity: organs, and organ systems, which are specialized fo gan? What is an organ system Mammalian body The four primary tissues of the vertebrate adult derived from three embryonic germ layer herve-are connective 49.2 Epithelial tissue forms membranes and glands Epithelial membranes cover all body surfaces 2. What are the different types Epithelial tissue Stratified membranes, particularly the keratinized ep thelial membranes and how Epithelial glands epider mis, provides protection, do they differ in structure and whereas simple membranes are more adapted for se- tunction cretion and transport. 3. What are the two types of Exocrine glands secrete into ducts that conduct the glands, and how do they differ in structure and function secretion to the surface of an epithelial membrane endocrine glands secrete hormones into the blood. 49.3 Connective tissues contain abundant extracellular material Connective tissues are characterized by abundant ex- 4. What feature do all connective tracellular matrix, which is composed of fibrous pro- issues share? What are the dif- teins ane d a gel-like ground substance in connective ferent categories of connective tissue? Give an example of each. Loose connective tissues contain many cell types such 5. What is the structure of a liga- as adipose cells and mast cells; dense regular connec ment? How do cartilage and tive tissues form tendons and ligaments bone differ? Why is blood con- Special connective tissues include cartilage d blood. Nutrients can diffuse through the matrix but not through the calcified matri which contains canaliculi for that purpose. 49.4 Muscle tissue provides for movement, and nerve tissue provides for control Smooth muscles are composed of spindle-shaped cells 6. From what embryonic tissue is d are found in the organs of the internal environ muscle derived? What two con Nerve tissue ment and in the walls of blood vessels tractile proteins are abundant in Muscle tissue Skeletal and cardiac muscles are striated; skeletal uscle? What are the three cate muscles,however, are under voluntary control gories of muscle tissue? Which whereas cardiac muscle is involuntary 7. Why are skeletal muscle fibers Neurons consist of a cell body with one or more den multinucleated? what is the drites and one axon. Neuron cell bodies form ga functional significance of interca and their axons form nerves in the peripheral lated discs in heart muscle? Neuroglia are supporting cells with various functions ncluding insulating axons to accelerate an electrical InfuSe 998 Part XIlI Animal Form and Function BioCourse. com
998 Part XIII Animal Form and Function Chapter 49 Summary Questions Media Resources 49.1 The bodies of vertebrates are organized into functional systems. • The vertebrate body is organized into cells, tissues, organs, and organ systems, which are specialized for different functions. • The four primary tissues of the vertebrate adult body—epithelial, connective, muscle, and nerve—are derived from three embryonic germ layers. 1. What is a tissue? What is an organ? What is an organ system? • Epithelial membranes cover all body surfaces. • Stratified membranes, particularly the keratinized epithelium of the epidermis, provides protection, whereas simple membranes are more adapted for secretion and transport. • Exocrine glands secrete into ducts that conduct the secretion to the surface of an epithelial membrane; endocrine glands secrete hormones into the blood. 2. What are the different types of epithelial membranes, and how do they differ in structure and function? 3. What are the two types of glands, and how do they differ in structure and function? 49.2 Epithelial tissue forms membranes and glands. • Connective tissues are characterized by abundant extracellular matrix, which is composed of fibrous proteins and a gel-like ground substance in connective tissue proper. • Loose connective tissues contain many cell types such as adipose cells and mast cells; dense regular connective tissues form tendons and ligaments. • Special connective tissues include cartilage, bone, and blood. Nutrients can diffuse through the cartilage matrix but not through the calcified matrix of bone, which contains canaliculi for that purpose. 4. What feature do all connective tissues share? What are the different categories of connective tissue? Give an example of each. 5. What is the structure of a ligament? How do cartilage and bone differ? Why is blood considered to be a connective tissue? 49.3 Connective tissues contain abundant extracellular material. • Smooth muscles are composed of spindle-shaped cells and are found in the organs of the internal environment and in the walls of blood vessels. • Skeletal and cardiac muscles are striated; skeletal muscles, however, are under voluntary control whereas cardiac muscle is involuntary. • Neurons consist of a cell body with one or more dendrites and one axon. Neuron cell bodies form ganglia, and their axons form nerves in the peripheral nervous system. • Neuroglia are supporting cells with various functions including insulating axons to accelerate an electrical impulse. 6. From what embryonic tissue is muscle derived? What two contractile proteins are abundant in muscle? What are the three categories of muscle tissue? Which two are striated? 7. Why are skeletal muscle fibers multinucleated? What is the functional significance of intercalated discs in heart muscle? 49.4 Muscle tissue provides for movement, and nerve tissue provides for control. • Art Activity: Mammalian body cavities • Epithelial tissue • Epithelial glands • Connective tissue • Tissues • Nerve tissue • Nervous tissue • Muscle tissue BIOLOGY RAVEN JOHNSON SIX TH EDITION www.mhhe.com/raven6ch/resource28.mhtml
50 Locomotion Concept outline 50.1 A skeletal system supports movement in animals. Types of Skeletons. There are three types of skeletal found in animals: hydrostatic skel exoskeletons, and endoskeletons. Hydrostatic skeletons Exoskeletons are made of tough exterior coverings on hich muscles attach to move the body. Endoskeletons are rigid internal bones or cartilage which move the body by the contraction of muscles attached to the skeleton The Structure of Bone. The human skeleton, an example of an endoskeleton, is made of bone that contains cells called osteocytes within a calcified matrix 50.2 Skeletal muscles contract to produce movements Types of Joints. The joints where bones meet may be movable, slightly movable, or freely movable Actions of Skeletal Muscles. Synergistic and antagonistic muscles act on the skeleton to move the bod FIGURE 50.1 0.3 Muscle contraction powers animal locomotion On the move. The movements made by this sidewinder attlesnake are the result of strong muscle contractions acting on The Sliding Filament Mechanism of Contraction. the bones of the skeleton. Without muscles and some type of Thick and thin myofilaments slide past one another to keletal system, complex locomotion as shown here would not be The Control of Muscle Contraction. During contraction Ca* moves aside a regulatory protein which had been preventing cross-bridges from attaching to the thin filaments Nerves stimulate the release of cat+ from its P lants and fungi move only by growing, or as the passive storage depot so that passengers of wind and water. Of the three multicellu- Types of Muscle Fibers. Muscle fibers can be lar kingdoms, only animals explore their environment in an categorized as slow-twitch(slow to fatigue) or fast-twitch active way, through locomotion. In this chapter we exam (fatigue quickly but can provide a fast source of power) ine how vertebrates use muscles connected to bones to Comparing Cardiac and Smooth Muscles. Cardiac achieve movement. The rattlesnake in figure 50.1 slithers muscle cells are interconnected to form a single functioning across the sand by a rhythmic contraction of the muscles unit. Smooth muscles lack the myofilament organization found in striated muscle but they still contract via the their legs. Although our focus in this chapter will be on sliding filament mechanism vertebrates, it is important to realize that essentially all ani Modes of Animal locomotion mals employ muscles. When a mosquito flies, its wings are straight lines. Their movements a d both by moved rapidly through the air by quickly contracting mechanical feedback and by neural Muscles generate power for movement, and also act as springs, movement is driven by strong muscles pus h the soi &.&su muscles. when an earthworm burrows thro ing its body brakes, struts hock absorbers
999 50 Locomotion Concept Outline 50.1 A skeletal system supports movement in animals. Types of Skeletons. There are three types of skeletal systems found in animals: hydrostatic skeletons, exoskeletons, and endoskeletons. Hydrostatic skeletons function by the movement of fluid in a body cavity. Exoskeletons are made of tough exterior coverings on which muscles attach to move the body. Endoskeletons are rigid internal bones or cartilage which move the body by the contraction of muscles attached to the skeleton. The Structure of Bone. The human skeleton, an example of an endoskeleton, is made of bone that contains cells called osteocytes within a calcified matrix. 50.2 Skeletal muscles contract to produce movements at joints. Types of Joints. The joints where bones meet may be immovable, slightly movable, or freely movable. Actions of Skeletal Muscles. Synergistic and antagonistic muscles act on the skeleton to move the body. 50.3 Muscle contraction powers animal locomotion. The Sliding Filament Mechanism of Contraction. Thick and thin myofilaments slide past one another to cause muscle shortening. The Control of Muscle Contraction. During contraction Ca++ moves aside a regulatory protein which had been preventing cross-bridges from attaching to the thin filaments. Nerves stimulate the release of Ca++ from its storage depot so that contraction can occur. Types of Muscle Fibers. Muscle fibers can be categorized as slow-twitch (slow to fatigue) or fast-twitch (fatigue quickly but can provide a fast source of power). Comparing Cardiac and Smooth Muscles. Cardiac muscle cells are interconnected to form a single functioning unit. Smooth muscles lack the myofilament organization found in striated muscle but they still contract via the sliding filament mechanism. Modes of Animal Locomotion. Animals rarely move in straight lines. Their movements are adjusted both by mechanical feedback and by neural control. Muscles generate power for movement, and also act as springs, brakes, struts, and shock absorbers. Plants and fungi move only by growing, or as the passive passengers of wind and water. Of the three multicellular kingdoms, only animals explore their environment in an active way, through locomotion. In this chapter we examine how vertebrates use muscles connected to bones to achieve movement. The rattlesnake in figure 50.1 slithers across the sand by a rhythmic contraction of the muscles sheathing its body. Humans walk by contracting muscles in their legs. Although our focus in this chapter will be on vertebrates, it is important to realize that essentially all animals employ muscles. When a mosquito flies, its wings are moved rapidly through the air by quickly contracting flight muscles. When an earthworm burrows through the soil, its movement is driven by strong muscles pushing its body past the surrounding dirt. FIGURE 50.1 On the move. The movements made by this sidewinder rattlesnake are the result of strong muscle contractions acting on the bones of the skeleton. Without muscles and some type of skeletal system, complex locomotion as shown here would not be possible
50.1 A skeletal system supports movement in animals. Types of Skeletons Animal locomotion is accomplished through the force of muscles acting on a rigid skeletal system. There are three dmmm;工 types of skeletal systems in the animal kingdom: hydraulic 功时一D skeletons. exoskeletons and endoskeletons dD口 Hydrostatic skeletons are primarily found in soft odie invertebrates such as earthworms and jellyfish. In this case, a fluid-filled cavity is encircled by muscle fibers As the muscles contract, the fluid in the cavity moves and hanges the shape of the cavity. In an earthworm, for ex- FIGURE 50.2 ample, a wave of contractions of circular muscles begins Locomotion in earthworms. The hydrostatic skeleton of the anteriorly and compresses each segment of the body, so earthworm uses muscles to move fluid within the segmented body that the fluid pressure pushes it forward. Contractions or cavity changing the shape of the animal. When an earthworm's longitudinal muscles then pull the rear of the body for circular muscles contract, the internal fluid presses on the Exoskeletons surround the body as a rigid hard case the earthworms. A wave of contractions down the body of the or ward(figure 50.2) longitudinal muscles, which then stretch to elongate segments in most animals. Arthropods, such as crustaceans and in earthworm produces forward movement. sects, have exoskeletons made of the polysaccharide chitin (figure 50.3a). An exoskeleton offers great protection to internal organs and resists bending. However, in order to ow, the animal must periodically molt. During molt- Chitinous outercovering ing, the animal is particularly vulnerable to predation be- cause its old exoskeleton has been shed. Having an exo- skeleton also limits the size of the animal. An anima with an exoskeleton cannot get too large because its ex- skeleton would have to become thicker and heavier. in a)Exoskeleton order to prevent collapse, as the animal grew larger. If an sect were the size of a human being, its exoskeleton Skull Scapula Ribs Vertebral column would have to be so thick and heavy it would be unable to move Endoskeletons. found in vertebrates and echino derms., are rigid internal skeletons to which muscles are Femur attached. Vertebrates have a flexible exterior that accom- Humerus Tibia modates the movements of their skeleton. The en doskeleton of vertebrates is composed of cartilage or one. Unlike chitin, bone is a cellular, living tissue capa Radius ble of growth, self-repair, and remodeling in response to hysical stresses (b)Endoskeleton The vertebrate skeleton FIGURE 50.3 Exoskeleton and endoskeleton.(a) The hard, tough outcovering A vertebrate endoskeleton(figure 50. 3b) is divided into a of an arthropod, such as this crab, is its exoskeleton. (6) BoRal and an appendicular skeleton. The axial skeleton's Vertebrates, such as this cat, have endoskeletons. The axial ones form the axis of the body and support and protect skeleton is shown in the peach shade, the appendicular skeleton the organs of the head, neck, and chest. The appendicular the yellow shade. Some of the major bones are labeled skeleton,s bones include the bones of the limbs and the pectoral and pelvic gir rdles tha attach them to the axial skeleton The bones of the skeletal system support and protect the There are three types of animal skeletons: hydrostatie body, and serve as levers for the forces produced by con- skeleton, exoskeleton, and endoskeleton. The traction of skeletal muscles blood cells form within the endoskeletons found in vertebrates are composed of ne marrow and the calcified matrix of bones acts as a bone or cartilage and are organized into axial and reservoir for calcium and phosphate ions appendicular portions 1000 Part XIlI Animal Form and Function
There are three types of animal skeletons: hydrostatic skeleton, exoskeleton, and endoskeleton. The endoskeletons found in vertebrates are composed of bone or cartilage and are organized into axial and appendicular portions. 1000 Part XIII Animal Form and Function Types of Skeletons Animal locomotion is accomplished through the force of muscles acting on a rigid skeletal system. There are three types of skeletal systems in the animal kingdom: hydraulic skeletons, exoskeletons, and endoskeletons. Hydrostatic skeletons are primarily found in softbodied invertebrates such as earthworms and jellyfish. In this case, a fluid-filled cavity is encircled by muscle fibers. As the muscles contract, the fluid in the cavity moves and changes the shape of the cavity. In an earthworm, for example, a wave of contractions of circular muscles begins anteriorly and compresses each segment of the body, so that the fluid pressure pushes it forward. Contractions of longitudinal muscles then pull the rear of the body forward (figure 50.2). Exoskeletons surround the body as a rigid hard case in most animals. Arthropods, such as crustaceans and insects, have exoskeletons made of the polysaccharide chitin (figure 50.3a). An exoskeleton offers great protection to internal organs and resists bending. However, in order to grow, the animal must periodically molt. During molting, the animal is particularly vulnerable to predation because its old exoskeleton has been shed. Having an exoskeleton also limits the size of the animal. An animal with an exoskeleton cannot get too large because its exoskeleton would have to become thicker and heavier, in order to prevent collapse, as the animal grew larger. If an insect were the size of a human being, its exoskeleton would have to be so thick and heavy it would be unable to move. Endoskeletons, found in vertebrates and echinoderms, are rigid internal skeletons to which muscles are attached. Vertebrates have a flexible exterior that accommodates the movements of their skeleton. The endoskeleton of vertebrates is composed of cartilage or bone. Unlike chitin, bone is a cellular, living tissue capable of growth, self-repair, and remodeling in response to physical stresses. The Vertebrate Skeleton A vertebrate endoskeleton (figure 50.3b) is divided into an axial and an appendicular skeleton. The axial skeleton’s bones form the axis of the body and support and protect the organs of the head, neck, and chest. The appendicular skeleton’s bones include the bones of the limbs, and the pectoral and pelvic girdles that attach them to the axial skeleton. The bones of the skeletal system support and protect the body, and serve as levers for the forces produced by contraction of skeletal muscles. Blood cells form within the bone marrow, and the calcified matrix of bones acts as a reservoir for calcium and phosphate ions. 50.1 A skeletal system supports movement in animals. FIGURE 50.2 Locomotion in earthworms. The hydrostatic skeleton of the earthworm uses muscles to move fluid within the segmented body cavity changing the shape of the animal. When an earthworm’s circular muscles contract, the internal fluid presses on the longitudinal muscles, which then stretch to elongate segments of the earthworms. A wave of contractions down the body of the earthworm produces forward movement. Chitinous outercovering Vertebral column Pelvis Femur Tibia Fibula Ulna Radius Humerus Skull Scapula Ribs (a) Exoskeleton (b) Endoskeleton FIGURE 50.3 Exoskeleton and endoskeleton. (a) The hard, tough outcovering of an arthropod, such as this crab, is its exoskeleton. (b) Vertebrates, such as this cat, have endoskeletons. The axial skeleton is shown in the peach shade, the appendicular skeleton in the yellow shade. Some of the major bones are labeled